The broad, long-term objective is to study the interaction between attention and motion processing that enables one to efficiently integrate, segment, and maintain a unified percept of moving surfaces. The guiding hypothesis: Visual attention is primarily "surface-based". It is directed to an entire surface, not particular features, facilitating the formation of a coherent representation of the attended surface, while suppressing unattended visual front. This hypothesis also holds that: even through attention is directed to a surface, which is a constellation of features chunked together by bottom-up mechanisms, processing is indirectly facilitated in lower-level units through feedback connections from surface-level mechanisms to the feature analyzers that subserves them. Targeting motion processing allows to take advantage of the motion after-effect (MAE), a powerful tool for measuring the processing of motion stimuli. SPECIFIC AIM 1. Isolate the effects of facilitatory mechanisms responsible for attentional modulation of motion processing. The relative strength of these effects, and their dependence on the low-level properties of the attended stimuli, will be investigated by measuring attentional effects on the MAE. SPECIFIC AIM 2. The hypothesis that attentional effects on motion processing, hence on the MAE, are due to selective enhancement of an entire surface, and not particular motion components, will be tested. Differences in attentional effects will be studied when attention is engaged in an irrelevant, non-motion task performed on an aspect of the stimulus which lies on the same surface as the adaption motion, or on a distinct surface. Specific aim 3. The hypothesis that attention is involved in the formation of surfaces will be tested. Special stimuli will be used, where local motion direction is modified by global surface formations. If attention is involved in surface formation, the normally global MAE direction will change to local when attention is distracted by a foveal task during adaptation.